Internet Engineering Task Force T. Narten
Internet-Draft J. Johnson
Intended status: Standards Track IBM
Expires: August 8, 2011 February 4, 2011
Definition of the UUID-based DHCPv6 Unique Identifier (DUID-UUID)draft-ietf-dhc-duid-uuid-03
Abstract
This document defines a new DHCPv6 Unique Identifier (DUID) type,
called DUID-UUID. DUID-UUIDs are derived from the already
standardized UUID format. DUID-UUID makes it possible for devices to
use UUIDs to identify themselves to DHC servers and vice versa.
UUIDs are globally unique and readily available on many systems,
making them convenient identifiers to leverage within DHCP.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 8, 2011.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
Narten & Johnson Expires August 8, 2011 [Page 1]

Internet-Draft DUID-UUID February 20111. Introduction
DHCP Unique Identifiers (DUIDs) are used in DHCPv6 to identify
clients and servers. This document defines a new DHCP Unique
Identifier (DUID) type that embeds a Universally Unique IDentifier
(UUID) [RFC4122]. UUIDs are already in wide spread use and serve as
an existing identifier that could be leveraged by DHCPv6. For
example, x86 based systems ship with an embedded UUID in firmware
that is readily available to the software running on the device.
Although DUIDs are new to DHCPv6, identifying clients in DHCP via a
UUID is not. DHCPv4 [RFC2132] defines a Client Machine Identifier
Option (option 97) that embeds a UUID (aka GUID) [RFC4578]. This
document extends that capability to DHCPv6.
Terminology specific to IPv6 and DHCPv6 are used in the same way as
is defined in the "Terminology" sections of [RFC3315].
2. Background
In DHCPv6, clients identify themselves to servers via DHCP Unique
Identifiers (DUIDs) [RFC3315]. DUIDs are identifiers that DHCP
servers treat as opaque objects with no internal structure. DUIDs
are intended to be globally unique, with no two devices using the
same DUID. Three DUIDs types have been defined previously:
DUID-LLT - the Link-Layer address of one of the device's network
interfaces, concatenated with a timestamp
DUID-EN - an Enterprise Number plus additional information specific
to the enterprise
DUID-LL - the Link-Layer address of one of the device's network
interfaces
DUIDs are intended to remain constant over time, so that they can be
used as permanent identifiers for a device. In the case of DUID-
LLTs, they are intended to be generated once, and then stored in
stable storage and reused from that point forward.
One issue that has arisen concerns devices that employ multi-step
network boot loading. An initial step (typically run out of
firmware) loads a small image that in turn loads a second image, and
so forth, until the actual target system is loaded. Each step in the
booting process may invoke DHCP. In some operational environments,
it is important that each step in the sequence use the same DUID, so
that the server knows it is getting requests from the same device and
Narten & Johnson Expires August 8, 2011 [Page 3]

Internet-Draft DUID-UUID February 2011
can return the proper configuration information (including the
pointer to the correct image to load).
Unfortunately, none of the previously defined DUIDs are ideal for
multi-step network booting. The DUID-LLT and DUID-LL identifiers
that a given device may use are not guaranteed to remain constant
across each booting step. Even if the different stages used DUID-LL
or DUID-LLT, on devices with multiple interfaces, there is no way to
guarantee that the same interface (and hence DUID) will be selected.
Finally, in the case of DUID-LLT, even if the same interface were
chosen, it can be difficult to ensure that each stage uses the same
timestamp value. While a DUID-EN could be defined and used, such
usage is proprietary by definition.
This document defines a new DUID type, based on the Universally
Unique IDentifier (UUID) [RFC4122]. UUIDs are already used in
practice and serve as an existing identifier that could be leveraged
by DHCP. In some environments, a UUID-based DUID is preferable to
the other existing DUID types.
It should be noted that use of a DUID-UUID will not by itself solve
all the network boot problems described in this document. Given the
availablility of a suitable DUID-UUID, implementations will still
need to take steps to ensure that all boot stages use the same DUID-
UUID as appropriate. Given that DHCP has already defined multiple
DUID types, the question of which of several DUIDs to select from
already exists -- and defining a new DUID type doesn't by itself
help. It is believed, however, that network boot services can be
configured to use a DUID-UUID and that other software can do so as
well. Ensuring this happens in general is beyond the scope of this
document.
3. UUID Considerations
Although many UUIDs are in use today, not all UUIDs meet DHCP's
requirements (see Section 9 of [RFC3315]). DHCP UUIDs should be
persistant across system restarts, across system reconfiguration
events, system software and operating system upgrades or
reinstallation, and be easily available to any part of the boot
process that requires access to the DHCP UUID. For example, UUIDs
used in Microsoft's Component Object Module (COM), and for labeling
partitions in filesystems, are likely not appropriate as they may not
be accessible to firmware boot loaders, and can change over time.
Implementations of this specification using DUID-UUID must select a
UUID that is persistent across system restart and reconfiguration
events, and that is available to all DHCP protocol agents that may
Narten & Johnson Expires August 8, 2011 [Page 4]

Internet-Draft DUID-UUID February 2011
need to identify themselves. For instance, a UUID that is part of
the system firmware, or managed by the system firmware, satisfies
this requirement.
4. DUID-UUID Format
The DUID-UUID is carried within Client Identifier or Server
Identifier options. It has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DUID-Type (4) | UUID (128 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
| |
| -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
DUID-UUID format.
Figure 1
DUID-Type - DUID-UUID (4) - (16 bits)
UUID - An RFC4122 UUID (128 bits)
5. Acknowledgements
This document was inspired by a discussion on the DHC mailing list in
November, 2009 on the topic of netboot for IPv6. Specifically, some
scenarios were described where it was difficult to do something in
DHCPv6 that had worked well in DHCPv4.
We would like to thank the following individuals in particular for
their specific comments and suggestions on this draft: Thomas Huth,
Andre Kostur, Suresh Krishnan, Ted Lemon, Bernie Volz & Vincent
Zimmer.
6. IANA Considerations
IANA has assigned the value 4 for use by the DHCPv6 DUID-UUID type.
[TO BE REMOVED UPON PUBLICATION: IANA should update the registry
entry for the DUID-UUID DUID-Type and mark the assignment permanent.]
Narten & Johnson Expires August 8, 2011 [Page 5]